Abstract:  Baiyun sag is one of the main oil and gas producing areas in the northern continental margin of the South China Sea. It has been widely discussed by scholars wroldwide because of its broad oil and gas prospects. However, the tectonic background, source rock composition, ancient water system, and ancient landform characteristics of the Eocene sedimentary source area need to be further studied. The evolution of the source system during the depression-fault-depression transition period is still not clear. In this paper, the characteristics of paleogeomorphology evolution and provenance distribution of Eocene in Baiyun sag  are systematically revealed based on rock mineralogy, rare earth element, and three-dimensional seismic data.  The results show that the tectonic background of the source area in Wenchang and Enping periods has the attribute of recycled orogenic belt, and the deposition of Enping Formation is restricted by the mixed orogenic belt and the stable continental block source area, which shows the characteristics of mixed source in the fault-depression transition period. In addition, the proportion of deep rock minerals such as rutile/garnet is higher in the Enping Formation, which may indicate strong tectonic metamorphism in the source area. The characteristics of rare earth elements show that the distribution patterns of Eocene source rocks and granites in Baiyun sag are similar. The ancient water system transits clockwise from convergence to divergence in the depression-fault-depression transition period. The source supply generally shows the characteristics of axial supply in the basin-the supply of the northern gentle slope-the long axis supply outside the basin. The characteristics of the lake basin also show the characteristics of small basin shallow lake-large basin deep lake-wide gentle lake basin-shallow water wide basin.

Key words:  , Pearl River Mouth basin, Baiyun sag, rare earth elements, ancestral river, ancient landscape, systems of provenance